Radiation detectors are devices capable of detecting incoming radiation. In medicine, radiation detectors for X-ray images have large applications for diagnosis of a patient's condition. The radiation detectors for X-ray images are typically integrated in radiological instruments that utilize computer-processed X-ray images to produce images of specific areas of a patient's body. These images may be planar images, panoramic images or so-called tomographic images. Planar images are typically obtained by flat panel radiation detectors. Panoramic images may be obtained by a sequence of planar images taken one after another. Tomographic images may instead be obtained by a three-dimensional reconstruction of the specific area of the patient's body. The radiological instruments may be intra-oral radiologic dental imagers, dental imagers, computed tomography scanners (CT-scanner), computed axial tomography scanners (CAT-scanners), mobile C-arm, etc. The radiation detectors for X-ray images usually consist of a radiation converter element (e.g. a scintillator) that absorbs and converts the incoming radiation (i.e. X-rays) into converted radiation with longer wavelength (e.g. photons). The converted radiation with longer wavelength reaches a photo sensitive element, e.g. a CMOS photosensor, a CCD image sensor, etc. The photo sensitive element may be coupled to an electronic system that generates electrical signals corresponding to a radiation pattern of the incoming radiation absorbed by the radiation converter element. Data embodied in such electrical signals may be shown in a visual display or sent to a computer for further analysis of the radiation pattern.
The radiation converter element used in the flat panel radiation detectors for X-ray images is usually a CsI (Caesium Iodide) scintillator. In fact CsI scintillators are highly efficient radiation converter elements in the X-ray range. CsI scintillators are capable of absorbing radiation in the X-ray range with high efficiency, preventing that the radiation hits the photo sensitive element, i.e. CsI scintillators have a so called high stopping power. Integration of the CsI scintillator in the flat panel radiation detector requires consideration of a series of factors. Among these factors a lifetime of the flat panel radiation detector ranging between 5 to 10 years must be guaranteed. The CsI scintillator is a part of the flat panel radiation detector most sensitive to lifetime degradation. This is due to the fact that the CsI scintillator is a slightly hygroscopic material, i.e. a material able to attract and hold moisture (i.e. water molecules) from the surrounding environment. Large part of the lifetime degradation of the CaI scintillator depends on penetration of the moisture into the CsI scintillator. The penetration of the moisture into CsI scintillator causes a degradation of a spatial resolution of the CaI scintillator. A measure of this spatial resolution of CsI scintillator is a so-called modulation transfer function (MTF). For high levels of moisture penetrated into the CsI scintillator, the MTF decreases, decreasing also the lifetime of the CsI scintillator. Therefore penetration of moisture into the CaI scintillator and into scintillators in general must be prevented or limited. The regulation of the penetration of moisture is especially relevant in columnar CaI scintillators.
Display devices are other types of devices where the penetration of moisture (i.e. water molecules) must be prevented or limited. Display devices including organic light emitting diodes (OLED) or polymer light emitting diodes (PLED) are particularly sensitive to moisture. These display devices use an electro-luminescence (EL) element in which electric current applied to specific organic luminescent materials transform electricity into luminosity. As duration of use of these display devices increases, the penetration of moisture into the display devices may also increase. The penetration of moisture may cause a detachment between a metal electrode and the organic luminescent material and/or an oxidation of the metal electrode. As a consequence a “dark-spot” in the display device may be formed to which electricity is not supplied. The “dark-spot” may appear as a decrease luminescence or luminescence uniformity of the display device.
Several solutions exist to prevent or limit moisture penetration into radiation detectors for X-ray images or into above-mentioned display devices.
In US20110121185A1a radiation image detecting apparatus is disclosed. The radiation image detecting apparatus is provided with a scintillator panel comprising a phosphor layer on a substrate and a photoelectric conversion panel. The scintillator panel is covered with a moisture protective layer. The scintillator panel is held between the photolelectric conversion panel and an opposed based material. A periphery of the photoelectric conversion panel adheres to a periphery of the opposed based material with an adhesive. Sealing of the scintillator panel is provided with the adhesive with controlled moisture permeability. In a space between the photoelectric conversion panel and the opposed base material a gas with a pressure lower than the atmospheric pressure is provided. The combination of the moisture protective layer of the scintillator panel and of the sealing with the adhesive makes the radiation image detecting apparatus moisture-resistant.
In US20030066311A1 a display element is disclosed. The display element can be used in OLED/PLED. The display element has a luminescent body formed on a glass substrate and a glass cap. The glass substrate and the glass cap are sealed together with a sealing layer of frit. The luminescent body is encapsulated in a structure formed by the glass substrate, the glass cap and the sealing layer of frit. In addition to that, a method to encapsulate the luminescent body is disclosed.
A problem with above-mentioned prior-art is that the radiation image detecting apparatus or display element needs to be sealed or encapsulated in some sort of case or housing to keep the radiation image detecting apparatus or display element moisture-tight.
Another problem with above-mentioned prior-art is that an adhesive or a sealing layer is needed on at least a periphery of the radiation image detecting apparatus or display element to form a tight sealing space surrounding the radiation image detecting apparatus or the display element. The adhesive or the sealing layer needs to be carefully chosen for its moisture permeability. Furthermore the periphery's area over which the adhesive or the sealing layer needs to be applied is significantly large. In addition to that, during temperature variations or temperature cycles used in a fabrication process of the radiation image detecting apparatus or the display element, the adhesive or the sealing layer or the moisture-tight housing may crack if a thermal expansion coefficient of the adhesive or the sealing layer or the moisture-tight housing does not match a thermal expansion coefficient of other materials used for sealing the radiation image detecting apparatus or the display element. Similar temperature variations or temperature cycles may be also obtained during handling (e.g. shipment) and/or storage of the radiation image detecting apparatus or the display element.